Traversing a duct is the standard method for measuring air velocity in a duct to obtain the volume of air flowing through the duct. Duct traversal is a two step process. First, the duct is prepared to measure the velocity of air at predetermined coordinates within the duct and then the airflow at the predetermined coordinates is measured. To determine air volume, the average velocity is multiplied by the cross sectional area of the duct.
To prepare a rectangular duct for traverse, a predetermined number of holes are drilled at predetermined locations across the surface of the duct. To calculate the number and locations of the holes, the width and depth of the cross section of the duct at the point of the traverse is measured using a ruler or tape rule. Once the number and the location of the holes are calculated, the positions of the holes are marked on the duct and thereafter the holes are drilled.
To measure the air velocity at the predetermined coordinates, a measuring probe connected to a velocity measuring instrument is inserted into the holes, one hole at a time. More specifically, before measuring the air velocity at the predetermined coordinates, the spacing of the coordinates in the duct is marked on the measuring probe. When the probe is inserted into the duct through a hole, it is oriented to a specific direction within the duct. Then, the air velocity is measured by moving the probe to each predetermined coordinates using the marks on the probe as reference. For accurate measurement, the probe is required to maintain a specific orientation within the duct during each measurement. This process is continued until the airflow has been measured through each hole.
Because ducts are generally installed overhead, duct traversal is generally most convenient from the bottom of a duct. But, holding a tape rule to the bottom of a duct to measure and mark the positions of the holes is very challenging. It also is very difficult to drill the holes and prevent the drill bit from walking. These tasks are made even more difficult because they are performed while standing on a ladder and looking upwards. In addition, using duct traverse reference materials and calculating the coordinates could be very tasking in field conditions.
While measuring the velocity, a technician is required to orient the probe to predetermined coordinates using the marks on the probe as reference as he pushes the probe Into the duct looking up. This process also takes place while the technician is standing on a ladder with the flow reading instrument dangling from his neck.
Although some ducts are installed at an angle, the traversing process is still the same. Developing a practical process or device to accurately determining the air volume in a duct based on the theory of duct traversing has not been achieved due to difficulties associated with duct traversal as discussed above. Consequently, due to the imprecise manner in which duct traversal is performed, the air volume calculated for a particular duct will be different each time air volume is calculated.
As discussed above, the process of duct traversal is inefficient and laborious, and multitasking on a ladder makes duct traversal unsafe. Embodiments of the present invention address these problems.